1. Field of the Invention
The present invention generally relates to assembling large area flat panel displays and, more particularly, to a chuck for assembling a plurality of smaller display areas, or xe2x80x9ctilesxe2x80x9d to form a larger display.
2. Description of the Related Art
Ever larger and flatter display screens are the trend in the display arts. Large, flat screen television and computer displays in particular are in high demand. Bulky cathode ray tubes (CRT), which have provided the basis for traditional displays, are slowly being replaced by thin film transistor (TFT) display technologies. TFT displays are now common in many portable computer applications and are even making an appearance in home theater systems. In comparison to CRT screens, TFT screens are light weight, use less energy, and are flat. In addition, high resolution, high contrast, and good visibility from a wide viewing angle make TFT displays the choice for the emerging high definition television (HDTV) format.
A drawback of TFT displays, and particularly TFT liquid crystal displays (LCD), is a high manufacturing cost and relatively low yield for larger sizes. Therefore, tiling techniques have been developed wherein smaller displays or xe2x80x9ctilesxe2x80x9d are seamlessly connected to form a larger display area.
Assembly of relatively small liquid crystal display tiles into a larger, seamless display involves the precise mating of the LCD tiles between a cover plate and a back plate. A very critical aspect of the assembly is that the front surface of the tile (the viewing side), when bonded to the cover plate with transparent adhesive, must exhibit a uniform gap between it and the cover plate. This gap must be uniform within each tile and the same for all tiles (four tiles are typically used in an assembly). A typical gap is 0.004xc2x10.002 inches. If the gap is not consistent, the brightness of an image displayed on the completed LCD assembly will not be even across the whole display.
What makes achieving a precise gap difficult is thickness tolerances in the cover plate and tiles. Cover plates may be xc2x10.004xe2x80x3 and tiles can be xc2x10.003xe2x80x3. Also, there may be some warping in the cover plate and tiles since they are very thin, further adding to the challenge.
One solution would be to hold the cover plate flat on a vacuum chuck and the tiles on a similar chuck. This would flatten the components out. However, the problem is that the components are referenced to the surface that contacts the chucks, not the opposite sides. It is the opposite sides that need to be held to an accurate gap relative to each other. Measurement devices could be used to determine the actual position of the mating surfaces and, with precision placement based on these measurements, a controlled gap could be achieved. However, this is costly, slow, and requires the fabrication of very precise hardware.
It is therefore an object of the present invention to provide a linear clutch which allows a chuck to compliantly move for positioning of a workpiece and thereafter be securely locked in place with minimal force and positioning disturbance.
It is yet another object of the present invention to provide a chuck for assembling individual tiles for an LCD display.
The invention employs a special connection or linear clutch between the tile chuck and the tile chuck carrier. This allows each chuck to float in the axis perpendicular to the tile""s mating surface. The chuck has freedom to move linearly in this axis, and allows for pitch and roll motion as well. This floating connection can be turned on or off at will. Thus, a tile attached to the chuck can be lowered over a cover plate and the chuck will compliantly move for high mating tolerances. Thereafter, the clutch can be locked to fix the chuck in it""s current position. In this manner, the tile can be raised so that an adhesive can be applied to the cover plate. The tile can then be lowered back over the adhesive with the clutch locked and alignment maintained.